1. Field of the Invention
This invention is related to combination motor starters and more particularly to an integral motor controller wherein a single set of contacts controlled by two operators are used for operation and protection of the motor and the associated circuitry.
2. Description of the Prior Art
Prior art combination motor starters as exemplified by U.S. Pat. No. 3,638,157 issued to Z. J. Kruzic are provided with separate units which provided for motor starting and stopping, current interruption, and current limiting. It is old in the art to provide a plurality of motor control and circuit protection devices connected in series in a common enclosure for complete motor and circuitry protection. It is old in the art to provide a fuse switch motor starter combination comprising a contactor with series connected overload relays to automatically open the contactor during lower overload current caused by motor overload, current limiting fuses for interrupting high level fault current, and a manual operable switch for permitting manual opening and closing of the motor circuit. It is also old to provide a fuse-breaker combination motor starter comprising a contactor with overload relays for opening the motor circuit upon the occurrence of lower overload currents, a manually operable circuit breaker automatically operable to interrupt the motor circuit upon the occurrence of the low level to high level fault current, and current limiting fuses that operate upon the occurrence of a high level short circuit currents. Prior art motor starters normally comprise a load break device which usually has silver cadmium oxide contacts or the like for low contact resistance. A solenoid mechanism is used to open and close the contacts. Contacts are spring biased toward the open position and are automatically opened if system voltage is lost. Low to high level fault current protection is provided by a series connected molded case circuit breaker. The molded case circuit breaker can be a single break deion circuit breaker with an adjustable magnetic trip. For long life and durability, silver tungsten contacts are often used in the circuit breaker. The adjustable magnetic trip can be set to operate the breaker from 7 to 13 times overload current. The molded case circuit breaker is capable of numerous operation interrupting high overload current. For example, the breaker used on one starter having a 100 ampere rating can interrupt currents up to 15,000 amperes up to three times. Current limitation is provided by current limiting fuses connected in series with the contactor and molded case circuit breaker for protection against possible fault currents up to 100,000 amperes rms. In addition a thermal overload relay which can be adjusted to open the motor stater at currents below the molded case circuit breaker with an appropriate delay are provided. It is also common to provide a series connected disconnect switch.
In the prior art it is necessary to use a plurality of circuit protection and motor control devices to provide for complete protection and operation of the motor and associated circuit over the entire current range.